1. Field of the Invention
The present invention generally relates to a composite optical dividing device for use in an image display apparatus to divide a light into multiple light beams of different wavelengths.
2. Description of Related Art
A main purpose of optical dividing devices is, for example, to divide a white light into red. (R), green (G), and blue (B) light beams, or other color light beams. The design of the optical dividing mechanism and structure of the optical dividing device varies with the apparatus in which the optical dividing device is used. In prior arts, the red, green, and blue lights can be obtained by color filters (CF) of respective colors.
In a flat display, a backlight source is often used in combination with a spatial light modulator and a color filter to present full-color images. In an image sensor of a digital camera, a color filter is also used in combination with color difference calculation to reproduce the color of an original object. In larger systems such as a color video camera or a back projection TV, a three-plate or two-plate prism set or a color filter is used in combination with a collimated light source to present full-color images. When the color filter is used in such systems, because each shading pixel can only present a single primary color of the RGB three primary colors, about two-thirds of energy of the incident white light is absorbed, thus decreasing the efficiency of using the light and shortening the lifespan of the battery. In addition, fabrication of the color filter can be rather complex and more than one semiconductor photolithography processes are needed for each primary color, which results in a high cost.
The industry has been continuing the research of optical elements, for example, as a substitute for the color filter, which is expected to produce three primary color light beams that correspond to pixels of a display panel and are incident onto a liquid crystal layer at a right-angle while maintaining a high optical efficiency.